Nutrient availability in the soil-plant system is dictated by complex interactions between plant roots, soil microorganisms, chemical reactions and pathways of losses. The macronutrients required by the plant can be lost by chemical processes such as exchange, fixation, precipitation and hydrolysis, and physical processes such as leaching, runoff and volatilization. Nitrogen, phosphorus and potassium (NPK), which are required in large amounts for plants, are not adequately available in natural soils to support the sustained growth of plants. Therefore, these macronutrients (NPK) are needed to be applied externally through fertilizers. Water soluble conventional fertilizers typically result in a large amount of macronutrients being lost by leaching and evaporation. There is an increased interest in developing slow release fertilizers that release macronutrients to plants over time. Advantages of slow release fertilizers are improved efficiency and quality as the fertilizer is released over time thus providing sufficient quantities of macronutrients as required for higher crop yields. In addition, slow release fertilizers result in reduced environmental damage from leaching of macronutrients into water and emissions as gasses, compared to conventional water soluble fertilizers.
Macronutrients in fertilizers can be applied to the soil as a solid in the form of a powder or pellets or as a spray. The uptake of macronutrients by the plant needs to be compensated by their external application to the soil periodically. Nitrogen is a key macronutrient source in agriculture particularly for economic crops such as tea, rubber and coconut. Large amount of fertilizer is applied to the soil of the tea plant to improve the quality and the yield of the leaves produced. For example, a study in Japan (Yamada et al., Journal of Water and Environmental Technology, 7, 4, 331-340, 2009) reported that of the large amount of amount of nitrogen fertilizer applied to tea, only 12% of the nitrogen input was up taken by the plant and the rest was discharged to the environment.
Coconut plants require an equatorial climate with high humidity to grow. Coconut plants and trees are grown in different soil types such as laterite, coastal sandy, alluvial, and also in reclaimed soils of the marshy lowlands. One of the unique features of coconut trees and plants are that it tolerates salinity and a wide range of pH (from 5.0-8.0). In terms of fertilizer application, the amount of N, P, and K required varies according to the type of coconut plantation. In addition Mg may become important in some soils.
Therefore, one of the unsolved problems of fertilizer application is, in relation to the amounts of nitrogen applied to soil, the low Nitrogen Use Efficiency (NUE) by crops. This is because an excessive amount of nitrogen, up to 70%, is lost in conventional fertilizers due to leaching, emissions, and long-term incorporation by soil microorganisms. As such, supplying N macronutrient is critical in preventing the decline of productivity and profitability due to degradation and aging of tea plants (Kamau et al., Field Crops Research 1, 108, 60-70, 2008). Attempts to increase the NUE have so far met with little success.
US2006/0135365 discloses wood chips containing macronutrient salts for short term plant growth and release of macronutrients over a period of one week. U.S. Pat. No. 7,165,358 disclose woodchips as a substrate for macronutrients for plant growth. U.S. Pat. No. 2,714,553 disclose converting wood lignin to sugar and forming a urea-formaldehyde condensation product for macronutrient delivery. U.S. Pat. No. 6,900,162 discloses a composition containing nitrogen particles adhered by a binder degraded by soil moisture to provide for the slow release. U.S. Pat. No. 7,211,275 B2 discloses a sustained release composite of water soluble materials that are adsorbed onto an inorganic material and is released by acidic fluids in medical applications.
Solutions are needed to provide slow and sustained release macronutrient formulations for plant growth applications. Therefore, macronutrients incorporated into cavities present in wood could be used to provide slow and sustained release of macronutrients for plant growth.